1. Field of the Invention
The present invention generally relates to a display apparatus and, more particularly, to a projection apparatus and a light integration rod thereof.
2. Description of Related Art
Referring to FIGS. 1A and 1B, a conventional projection apparatus 100 includes a light source module 110, a projection lens 120, a digital micro-mirror device (DMD) 130 and a symmetrical light integration rod 140. The light source module 110 is suitable for providing an illumination beam 112. The DMD 130 is suitable for reflecting the illumination beam 112 into an image beam 132 traveling to the projection lens 120, and the illumination beam 112 is obliquely incident upon the DMD 130. The symmetrical light integration rod 140 is disposed on the transmission path of the illumination beam 112 and is a hollow rod composed of four reflective plates 142a, 142b, 142c and 142c with equal lengths. The symmetrical light integration rod 140 has a light input end 144a and a light output end 144b. The illumination beam 112 from the light source module 110 enters the symmetrical light integration rod 140 through the light input end 144a, and is reflected many times. Then, the illumination beam 112 is output through the light output end 144b and travels to the DMD 130.
Since the symmetrical light integration rod 140 has a symmetrical structure, the focal plane 114 of the illumination beam 112 traveling to the DMD 130 is perpendicular to the optical axis of the illumination beam 112. However, since the illumination beam 112 is obliquely incident upon the DMD 130, the focal plane 114 has an obliquity angle θ with respect to the DMD 130 and does not fall on the DMD 130. As such, parts of the illumination beam 112 striking both ends 134a and 134b of the DMD 130 away from the focal plane 114 would be defocused.
The above-mentioned defocusing causes two edges of the light spot formed by the illumination beam 112 projected on the DMD 130 to blur, wherein the two edges are respectively close to the ends 134a and 134b of the DMD 130. Considering the blurring portion of the light spot has nonuniform brightness and irregular shape, the blurring portion is not suitable for being projected onto the display region of the DMD 130, which results in wasting a part of the illumination beam 112, lowering the utilization ratio of the illumination beam 112 and further making the brightness of display pictures provided by the projection apparatus 100 hard to be improved.
FIG. 2 is a 3D-diagram of a conventional wedge light integration rod. Referring to FIGS. 1A and 2, in order to lighten the blur extent at the edges of the above light spot, the symmetrical light integration rod 140 in the projection apparatus 100 may be replaced by a wedge light integration rod 140′. The wedge light integration rod 140′ has an oblique light emitting section 142′ at the light output end 144b′ and the normal vector N of the light emitting section 142′ has an obliquity angle φ with respect to the optical axis C of the wedge light integration rod 140′. The obliquity angle φ is corresponding to the included angle between the optical axis of the illumination beam. 112 and the DMD 130. By adjusting the obliquity angle φ, the focal plane of the illumination beam 112 may coincide with the DMD 130 as much as possible to lighten the blur extent of the edges of the light spot formed by illumination beam 112 projected on the DMD 130. However, during fabricating the wedge light integration rod 140′, to make the light emitting section 142′ oblique, parts of plates, which compose the wedge light integration rod 140′, must be cut into trapezoid, which would increase the rest scrap after cutting. In addition, the cutting angle of the plates must be controlled quite precisely to make the focal plane of the illumination beam 112 coincide with the DMD 130 as much as possible. Therefore, the production cost of the wedge light integration rod 140′ is higher.